(1) Field of the Invention
The present invention relates generally to an air conditioning system mounted particularly in an automotive vehicle compartment wherein an emergency controller is incorporated for maintaining basic functions of the air conditioning system in addition to a means for adjusting a cooling or heating temperature and, more particularly, to the emergency controller incorporated in the air conditioning system whereby the basic functions of the maximum cooling and heating are maintained by switching the temperature adjusting means to the emergency controller in a case when the temperature adjusting means fails.
(2) Description of the Prior Art
Recently, most air conditioning system of an automotive vehicle have been provided with an automatic temperature adjusting means utilizing advanced electronics technology.
Since the automatic temperature adjusting means comprising an electronic control unit is used in a severe environment where a high resistance to heat and surge voltage is required, some measure must be taken in the air conditioning system against failure. In particular, if such electronic circuit fails, a emergency control means will be required which maintains the basic function of the air conditioning system, such as cooling the air at the maximum output and heating the air at the maximum output. Such emergency control means is usually provided separately from the automatic temperature adjusting means. Some of the emergency control means are put into practical use in the air conditioning system according to this demand from the user.
Two emergency control devices of the prior art are described hereinafter.
One of such emergency control devices comprises a temperature switch provided at the previous output stage of an electronic control circuit for feeding a current into either of a pair of driving transistors to drive the air conditioning system into either of the maximum cooling or heating conditions. In more detail, the temperature switch is located in parallel with a voltage comparator for comparing a temperature-proportional signal with a reference signal to output an automatic control signal and actuates either of the transistors at the last output stage of the electronic control circuit by means on a current signal of a separate power supply line and further actuates a double solenoid vacuum valve connected to the transistors so that maximum vacuum control output can be generated. Thus the double solenoid vacuum valve operates a vacuum power servo which is thus displaced up to a maximum stroke position. Consequently, a rapid switching into either of the maximum cooling or heating conditions can be made for a failure within the electronic control circuit. However, since the temperature switch is located at the previous output stage of the electronic control circuit, the temperature switch works effectively for a failure within the more previous stages from either of the transistors but can no longer perform its emergency measure for a failure of control parts, transistors, or double solenoid vacuum valve located at the successive stages therefrom.
The other emergency control device comprises a sub vacuum selector made of a mechanical element incorporated in a vacuum control circuit and connected to the vacuum power servo. In this air conditioning system, a vacuum output from a vacuum source is under automatic control by means of the electronic control circuit and a transducer. When trouble occurs in an electric circuit, the sub vacuum selector is used manually to fix a maximum cooling, or heating condition. In other words, the sub vacuum selector is operated so that the electronically controlled vacuum output is switched to a manually selectable vacuum output to supply the vacuum power servo with a vacuum output so as to open or close fully an air mixing door.
In this way, such an emergency control device has a feature that only a vacuum control circuit is operated to actuate the vacuum power servo without use of an electric circuit.
The sub vacuum selector comprises a pair of selector members brought in close contact with each other and provides a means for linking the vacuum valve with the double solenoid vacuum valve or vacuum power servo. Such linkage switch is performed by changing the relative angle between both selector members. However, since in the sub vacuum selector the tightly closed selector members are turned with an axle as a fulcrum, a large turning force is required during the manipulation and it is difficult to maintain complete air-tightness in the selector members so that erroneous operation accompanying the air leakage may result.